Radiation therapy is a form of treatment based on using ionizing radiations (x-rays or radioactivity, including gamma rays, electrons and accelerated particles). Said treatment is commonly used today in oncology treatments for curative or palliative purposes.
Radiation therapy is divided into three types according to the distance of the source of irradiation with respect to the object to be irradiated, these types being called external radiation therapy, brachytherapy and intraoperative radiation therapy.
Radiation therapy generally requires a dosimetric analysis (spatial distribution of the dose deposited in the patient) which is carried out from previously obtained computed tomography (CT or CAT, computed axial tomography) images which, when introduced in planning equipment, allow calculating the distribution of the dose from the radiology attenuation information they contain over the tissues in which it interacts.
Specifically, intraoperative radiation therapy (IORT) for which the method and system of the present invention are described, is a technique combining surgery and radiation therapy generally applied in patients with tumors for which surgical resection (extirpation) has been indicated and in patients who have a high risk of recurrence (return of the tumor), and it consist of directly applying a single radiation dose by means of electron beams, the patient being subjected to surgery in order to expose the targeted area and directly apply the radiation to it.
To that end the area to be irradiated is defined in the attempt to protect healthy tissues either by retracting or separating the rest of the surrounding organs that can be moved or by means of protecting the fixed organs with radiation-opaque elements.
Currently, although there are a number of dosimetry planning tools typically used for external radiation therapy and brachytherapy, this is not the case for IORT, in which given its special characteristics, said tools do not exist, leaving the calculation of the dose to be applied once the patient has already been subjected to surgery up to the surgeon or radiation oncologist and their experience, i.e., once said specialist has access to the tumor which is to be removed or reduced, which, as is evident, results in difficulties in the radiation therapy process and limits both its quality and the subsequent patient progress follow-up.
The reasons which prevent the existence of IORT planning and dosage tools are the difficulties due to the need for retracting or separating the surrounding organs during the surgical process, and due to the extirpation of the tissues concerned, which facts contribute to modifying the morphology of the patient with respect to that observed in the preoperative image studies. These modifications are very difficult to estimate beforehand during planning with the information from a preoperative CAT scan. Furthermore, said problem is even more considerable in the case of IORT, because the radiation is based on the emission of electrons, the dosimetry of which is much more dependent on the exact geometric distribution of the tissues than the radiation based on the emission of photons, which is more common in external radiation therapy.
Therefore, said difficulties translate into the following problems when planning:                Before the intervention: it is difficult to estimate the doses that each structure exposed to the radiation will receive.        During the intervention: dosimetry estimations adapted to surgical findings cannot be performed, such that the planning can be modified and how possible surgical approach alternatives would affect the dosimetry can be evaluated.        After the intervention: since quality control images taken during treatment are not available, as is the case of portal imaging (x-ray images acquired for comparison) in external radiation therapy, that would serve as evidence of the patient's situation during the application of the treatment, the process cannot be correctly evaluated and documented.        
Additionally, since it is an invasive technique in which a radiation applicator cone is introduced until it reaches the tissues to be irradiated, entry paths must be searched for and suitable positioning on the tumor bed sought.
As stated, until now it was up to the surgeon or radiation oncologist to decide, according to their intuition, medical and surgical experience, and based on the information generated during surgery, on aspects as fundamental as the diameter of the radiation beam applicator cone, the positioning thereof, the angle of its bevel and even the energy of the electrons.
This means that currently in IORT, a prior dosimetry estimation of the radiation that will be applied is not performed with suitable reliability (comparable to that which is currently obtained in external radiation therapy) and nor are the obtained results (complete extent of the tumor bed, radiation of healthy tissue, . . . ) evaluated or recorded, so the possible side effects can neither be explained nor referenced to the patient's medical history.
A professional who wishes to plan a method of IORT therefore needs a tool which allows estimating the distribution of the dose which will be deposited in the anatomical structures determined by said professional as a function of the different possible approaches. From the point of view of the professional who wishes to evaluate the results of an intervention already performed, it is desirable to further know the doses received in the different structures in order to thus explain and/or study the progress of the patient.
The documents existing in the state of the art do not solve these problems because they relate to the external radiation therapy process, as in the case of U.S. Pat. No. 3,987,281, or only to algorithms improving the dose calculation, such as U.S. Pat. No. 4,729,099 or U.S. Pat. No. 6,792,073 for example.
In other cases, different methods improving the planning by optimizing the number of treatment fields, the orientations of the mobile elements or the formation of the radiation beams have been developed, as in U.S. Pat. No. 7,266,175 or U.S. Pat. No. 7,202,486, but they solely and exclusively relate to the planning process and dose calculation in external radiation therapy.
Finally, there are also designs of several radiation beams with independent intensities, as in U.S. Pat. No. 5,647,663, or the integration of image types in the process, either a computed tomography for external radiation therapy, U.S. Pat. No. 5,651,043, or ultrasound in brachytherapy, U.S. Pat. No. 5,391,139, or works on the quality control of the process which try to reproduce the position of the patient during the different treatment sessions, as in U.S. Pat. No. 6,032,066, WO2007028237 or EP1758649, in some cases using radiation detectors to compare the process with the prior planning (U.S. Pat. No. 140,425 and U.S. Pat. No. 58,778).
However, none of the described systems is oriented towards intraoperative radiation therapy because they are systems integrated in the external radiation therapy process which do not allow reproducing the anatomical modifications experienced by the patient during the surgical process, or calculating the dosimetry for electron radiation in that particular situation of the patient.
There is a scientific paper in which some of the inventors collaborated (M. Desco, J. López, F. Calvo, A. Santos, F. del Pozo, P. Garcia-Barreno) “Simulated Surgery on Computed Tomography and Magnetic Resonance Images: An Aid for Intraoperative Radiotherapy”. Comput Aided Surg, 2(6):333-339, 1997) which presented only a joint graphic vision of image studies of the patient and isodose curves for electron radiation, without performing any precise dosimetry calculation or allowing a radiation therapy treatment simulation prior to the intervention, i.e., it is simply a work for displaying the isodose curves previously measured in a water phantom superimposed on the non-modified image studies.